For all types of substrates, magnetic recording media has begun to incorporate perpendicular magnetic recording (PMR) technology in an effort to increase areal density and is now working toward densities of 800 Gbits/in2. Generally, PMR media may be partitioned into two primary functional regions: a soft magnetic underlayer (SUL) and a magnetic recording layer(s) (RL). FIG. 1 illustrates portions of a conventional perpendicular magnetic recording disk drive system having a recording head 101 including a trailing write pole 102 and a leading return (opposing) pole 103 magnetically coupled to the write pole 102. An electrically conductive magnetizing coil 104 surrounds the yoke of the write pole 102. The bottom of the opposing pole 103 has a surface area greatly exceeding the surface area of the tip of the write pole 102. As the magnetic recording disk 105 is rotated past the recording head 101, current is passed through the coil 104 to create magnetic flux within the write pole 102. The magnetic flux passes from the write pole 102, through the disk 105, and across to the opposing pole 103 to record in the PMR layer 150. The SUL 110 enables the magnetic flux from the trailing write pole 102 to return to the leading opposing pole 103 with low impedance.
Typically, higher areal densities are typically achieved with well-isolated smaller grains in the PMR layer. A higher magnetocrystalline anisotropy constant (Ku) is typically required to resist the demagnetization effects of the perpendicular geometry and to keep the smaller grains thermally stable to reduce media noise. For example, smaller grain size (<7 nm) and high magnetocrystalline anisotropy (Ku) L10 ordered FePt media can achieve areal density beyond 1 Tb/in2 magnetic recording.
As such, some PMR media use antiferromagnetically-coupled soft magnetic underlayers (SULs), Ta seed layer and Ru intermediate layers to induce favorable crystallographic texture, define grain size and to produce a distinctive microstructure comprising isolated magnetic grains in a nonmagnetic matrix. To further assist with these desirable properties, some PMR media also use a Cr, CrTi or CrTa adhesion layer between the substrate and SUL, and a NiW-based orientation layer NiW, NiWAl, NiWAlFe) under the seed layer.
FIG. 2 illustrates a cross-sectional view of an exemplary PMR media comprising a bottom substrate 203, an adhesion layer 206, a SUL 209, an orientation interlayer 212, a seed layer 215, an intermediate layer 218, and a magnetic recording layer 221.
Enhanced write head fields and gradients are desirable in PMR media because (a) they help in writing data on the PMR media with higher switching fields, and (b) they help in overwriting previously written data on the PMR media. The writability for PMR media is traditionally measured in terms of reverse overwrite (referred to as OW or OW2), which is a recording parameter measured in decibels (dB).
Generally, a SUL (e.g., 215) provides a closure path for the magnetic flux from the magnetic write head to the PMR media during data writing processes, and provides the PMR media with sharp head field gradients and large head fields. Unfortunately, the intermediate and seed layers (e.g., 212 and 215 respectively) are typically non-magnetic (e.g., NiW and Ru, respectively) and as a consequence, diverge the write head flux leading to decreased write head fields and gradients. As such, to further enhance write head fields and gradients, some PMR media use NiWFe-based seed layers to improve media overwrite. NiWFe is magnetic and known to help pass the flux from the write head onto the SUL.